The non-hemolytic or "viridans" streptococci cause endocarditis, abscesses of the brain and internal organs, and septicemias. The presence of S. bovis in feces correlates with colon malignancies. Yet there is no universally accepted taxonomy of these bacteria. This complicates efforts to identify them. In many laboratories they remain unidentified. A better taxonomy, based on genetic relationships, would foster accurate and timely identification, facilitate epidemiology, and promote the development of new technology based on DNA "probes" for the rapid identification of these streptococci. Therefore, strains identified as, resembling, or possibly belonging to S. mitior, S mitis, S. milleri, S. sanguis, S. salivarius, and S. bovis will be collected from large clinically oriented microbiological laboratories. Recognized stock strains and type strains as well as recent clinical isolates will be acquired. The bacteria will be characterized by standard cultural and biochemical tests. DNA will be isolated from these cocci after cell crops are lysed with a combination of penicillin, lysozyme, and detergent. The base compositions of the DNAs will be determined by thermal denaturation, and the DNA base sequence similarities will be assessed by DNA-DNA hybridization on membrane filters or in solution. The streptococcal strains will be grouped into species based on the similarities of their DNA and then defined phenotypically by the biochemical and cultural characteristics which correlate best with the gentically defined species. In this way, the taxonomy of this important group of bacteria can be established on a molecular foundation and the relationships of these species can be defined more strictly. The overall goal is to aid clinicians in their efforts to help patients afflicted with these streptococci.